It is common in industry to produce linear mechanical motion directly through electromagnetic forces developed by a variety of linear electric motors. Linear induction motors are the most common among them. The principles of linear induction motors are well known: a three-phase winding of inductor generates a traveling electromagnetic field which induces eddy currents in the conducting layer of the induct and their interaction produces thrust in a lengthwise direction.
Despite lower energy conversion efficiency and power factor, the ruggedness of linear induction motors promotes a multitude of motor topologies for various applications. Flat and tubular topologies are the two basic classes.
Various types of tubular linear induction motors (T-LIM) are known in the art. They are commonly treated as low-speed linear induction motors with low excursion; lower than 1.5 to 2 meters. There are many well-known actuators with short-path reciprocating movement of induct. They are predominantly configured as a simple solid passive shaft moving inside the active stator which carries AC powered electrical windings (inductor). The mover can be complemented by permanent magnets. They have found application in, among others, compressors, pumps, and valves.
Examples of T-LIM actuators can be found in: U.S. Pat. No. 10,102,954 to Waterstredt at al., U.S. Pat. No. 9,935,536 to Rios-Quesada at al., U.S. Pat. No. 9,887,612 to Eghbal at al., U.S. Pat. No. 9,871,433 to Satou at al., U.S. Pat. No. 9,739,229 to Hutchins at al., U.S. Pat. No. 9,525,329 to Satau at al., U.S. Pat. No. 9,209,662 to Hsieh at al., U.S. Pat. No. 8,922,069 to Iwaki at al., U.S. Pat. No. 8,618,700 to Muramatsu at al., U.S. Pat. No. 8,106,545 to Homma at al., U.S. Pat. No. 7,958,908 to Cho at al., and U.S. Pat. No. 5,831,353 to Bolding at al.
There is a variety of other applications of T-LIM where short and precise linear motions are required—for example two or three coordinates stepper motors. The application of these motors is limited to short linear movements in the machine industry where precise positioning is essential.
Examples of these types of T-LIM can be found in: U.S. patent application Ser. No. 10/882,095 to Hoppe at al., U.S. Pat. No. 10,116,195 to Lu at al., U.S. Pat. No. 10,103,593 to Kano at al., U.S. Pat. No. 10,050,507 to Hofstetter at al., U.S. Pat. No. 10,044,251 to Masuzawa at al., U.S. Pat. No. 10,020,716 to Atmur at al., U.S. Pat. No. 9,973,065 to McAleese at al., U.S. Pat. No. 9,479,040 to Schaffel at al., U.S. Pat. No. 9,379,599 to Tang at al., U.S. Pat. No. 8,390,153 to Aso at al., U.S. Pat. No. 7,812,482 to Aso at al., U.S. Pat. No. 7,752,736 to Pulford at al., U.S. Pat. No. 6,354,224 to Devnani at al., U.S. Pat. No. 6,130,490 to Lee at al., U.S. Pat. No. 5,365,131 to Naito at al., U.S. Pat. No. 5,298,819 to Suganuma at al., and U.S. Pat. No. 5,276,293 to Narumi at al.
The existing T-LIMs in the art are not suitable for higher speeds and long traveling ranges required in transportation field.
Recent development in tubular transportation domain makes possible and attractive an application of some kind of tubular motor, like a tubular linear induction motor, which is by its topology well suited for the purpose.
Examples of high speed tubular transportation patents: U.S. Pat. No. 10,093,493 to Bambrogan at al., U.S. Pat. No. 10,086,846 to Dalrymple at al., U.S. Pat. No. 9,997,985 to Prussmeier at al., U.S. Pat. No. 9,764,648 to Finodeyev at al., U.S. Pat. No. 9,718,630 to Bambrogan at al., U.S. Pat. No. 9,604,798 to Bambrogan at al., U.S. Pat. No. 9,517,901 to Bambrogan at al., U.S. Pat. No. 9,511,959 to Bambrogan at al., U.S. Pat. No. 8,783,192 to Smith at al., U.S. Pat. No. 7,562,628 to Wamble at al., U.S. Pat. No. 6,374,746 to Fiske at al., U.S. Pat. No. 5,653,173 to Ficher at al., U.S. Pat. No. 5,388,527 to Thornton at al., U.S. Pat. No. 4,512,258 to Matsukata at al., U.S. Pat. No. 4,324,185 to Vinson at al., and U.S. Pat. No. 4,061,089 to Sawyer at al.